The present invention relates to a method for producing large crystal zeolite ZSM-5 from a reaction mixture containing a mixture of tetrapropylammonium (TPA) cations and tetramethylammonium (TMA) cations. The reaction mixture also includes a source of deliberately added alumina such as, for example, aluminum sulfate.
ZSM-5 has a distinctive X-ray diffraction pattern which distinguishes it from other known zeolites. The original alkali metal cations, if any, of ZSM-5 can be exchanged by ion exchange with other ions to form species of the zeolite which have exceptional catalytic properties. Zeolite ZSM-5 and its preparation are the subject of U.S. Pat. No. 3,702,886, the entire disclosure of which is expressly incorporated herein by reference. That patent discloses an average particle diameter of less than 1/2 micron.
U.S. Pat. No. 3,941,871, the entire disclosure of which is also expressly incorporated herein by reference, describes a method for preparing crystalline metal organosilicate ZSM-5 from reaction mixtures containing no deliberately added aluminum. However, as pointed out in column 4, lines 19-26 of this 3,941,871 patent, aluminum may be present in the reaction mixtures as impurities from other reactants and/or equipment used. For example, sources of silica contain aluminum impurities often in quite detectable but trace quantities. Accordingly, the organosilicates of the 3,941,871 are said to possibly contain readily detectable quantities of alumina, but in no event is the silica to alumina molar ratio of these organosilicates said to be less than or equal to 200. Example 5 of this 3,941,871 patent describes the preparation of ZSM-5 from reaction mixture containing both tetrapropylammonium (TPA) and tetramethylammonium (TMA) cations, but the reaction mixture does not contain a deliberately added source of alumina such as, e.g., aluminum sulfate.